1. Field of the Invention
The present invention relates generally to a data network having data processing devices linked for data transmission. In particular, the present invention relates to obtaining a reduction in the power consumed by data transceivers in such a network.
2. Background Art
Data transmission loops have been used in local area networks of data processing devices for coupling data terminals to a central processor. The loop topology permits each data terminal to monitor data transmitted over the loop, and to insert data into the loop. More recently, the loop topology has been proposed for connecting disk drives to a storage controller in a storage subsystem. In this application, the loop interfaces in a simple way to optical fibers interconnecting the storage controller to the disk drives, and the number of pin connections to the disk drives is reduced for enhanced reliability. Manufacturers of data processing devices and disk drives are presently cooperating in the development of standards for the transceivers, cables and connectors to be used in connecting loops of disk drives to data processing equipment. The data transmission loop has been named Fibre Channel Arbitrated Loop, and the current standards are described in Kurt Chan, FC-AL Direct Disk Attach Profile (Private Loop) Version 1.2, Hewlett-Packard, 9000 Foothills Blvd., Roseville, Calif. 95747-5601, Preliminary Draft Version, 1.20 (Jan. 4, 1995), incorporated herein by reference. One disadvantage of the Fiber Channel Arbitrated Loop is that all of the transceivers in the loop are running continuously. To avoid skews and to minimize the number of connections, data is transmitted serially over the loop. Consequently, it is desirable to transmit data at the highest practical rate, such as at 265.625 MHz, 531.25 MHz, or preferably 1.0625 GHz. Consequently, transceivers must consume a substantial amount of power in order to serialize and deserialize the data at such a high rate. For example, a 3 and 1/2 inch disk drive employing a standard SCSI interconnect consumes about 15 watts. The 3 and 1/2 inch drive, when adapted with Fiber Channel transceivers available in the first quarter of 1996, is expected to require no less than about 18 watts. Consequently, a disk array cabinet designed for the standard SCSI drives cannot be fully populated due to power supply and cooling limitations. The option of increasing the power supply and cooling capacity is undesirable since it would require a re-design of the power supply and cabinets, and would increase the cost of ownership, cost of air conditioning, and the cost of power.